The New York City mother who came home to find her two young children allegedly stabbed to death by a trusted nanny, then watched helplessly as the woman knifed herself in the throat and slit her wrists, police said today.

At a press conference today, Police Commissioner Ray Kelly said the nanny Yoselyn Ortega, 50, remains on a breathing tube after being rushed to a hospital Thursday evening, and has yet to be interviewed by cops or formally charged.

Kelly, and neighbors who knew the woman for years, said Ortega had no known history of mental illness.

"I'm in shock. It's out of this world. There was nothing to make me think she would do this. Nothing," said Marcelina Lovera, a neighbor who lived in the same Harlem apartment building where Ortega and her son resided.

The nanny, a naturalized U.S. citizen who was born in the Dominican Republic, worked for the Krim family for two years and had been referred to them by another family, the police commissioner said.

Ortega lives with her son and her sister. They are cooperating with police, Kelly said.

Outside the luxury building where the victims' lived, neighbors have created a makeshift memorial, laying flowers and leaving condolence messages for the distraught mother, Marina Krim and her husband Kevin Krim.

"We are weeping with you," read one note left outside the La Rochelle apartment building on Manhattan's affluent Upper West Side.

Marina Krim came home Thursday evening around 5:30 p.m., after taking her 3-year-old to a swim class at the YMCA. She arrived home to a dark and quiet apartment and initially thought the nanny had taken the children out.

Upon entering a bathroom, Marina discovered Ortega and her two other children Lucia, 6, and 2-year-old Leo dead in a bathtub filled with blood, authorities said.

It was at that moment that Ortega is believed to have slashed herself, Kelly said.

Ortega is in critical but stable condition and has no criminal record, police said.

A preliminary police investigation had not yet yielded a possible motive for the deaths.

The children's father, a CNBC executive, was on a business trip in San Francisco at the time of the murders. He flew home Thursday night and police picked him up at the airport and rushed him to his family, authorities said.

A neighbor who lives on the same floor in the building at 57 W. 75th St. near Columbus Avenue told the AP that she heard screams around 5:30 p.m.

"There was some kind of screaming about, 'You slit her throat!' It was horrible," said the neighbor, Rima Starr, a music therapist.

After police arrived, she told AP, the mother remained in the building's lobby, screaming hysterically and clutching her surviving child.

"[The mother was] crying out 'What am I going to do with the rest of my life? My life is ruined. I have no children, I have no children,'" neighbor Herbert Klein said.

Klein said he had met the nanny in the apartment building: "Once, I had the opportunity to say good morning cheerfully, and got no reply."

On a webpage devoted to a recent family wedding, the couple's daughter, nicknamed Lulu, was described as loving "art projects, ballet and all things princess." Her younger brother was said to be just learning how to walk.

Neighbors described the Krims as a vibrant, happy family.

"Young family. Busy family. Parties all the time and they have friends coming over," Klein said.

"A member of the CNBC family has suffered an unimaginable loss. The sadness that we all feel for Kevin, Marina and their family is without measure. Our thoughts, prayers and unwavering support are with them all, Comcast and NBC Universal said in a statement Friday morning.